Accounting for Telecommunications Terminal Mobility in Call Admission Control

ABSTRACT

A technique is disclosed to optimize the call admission control algorithm that governs a shared-communications channel, in which the algorithm accounts for the levels of mobility, on an individual basis, of one or more terminals that need to use the channel. Instead of determining the variation in the distribution of supported data rates aggregated across multiple terminals—which can result in a greater variance in the call admission criterion—the technique of the illustrative embodiment tracks the variation in the distribution, for each terminal, of the data rates for that terminal. In short, the technique of the illustrative embodiment accounts for the variance in data rates that is attributed to the mobility of individual, representative terminals and not to the variance that is attributed to the spatial distribution of multiple terminals.

REFERENCE TO RELATED APPLICATIONS

This application incorporates herein by reference the underlyingconcepts, but not necessarily the nomenclature, of U.S. patentapplication Ser. No. 11/317514, filed on 23 Dec. 2005, Attorney Docket630-157US, entitled “Call Admission Control for Mobility-CapableTelecommunications Terminals.”

FIELD OF THE INVENTION

The present invention relates to telecommunications in general, and,more particularly, to admitting a call in a shared-access system.

BACKGROUND OF THE INVENTION

FIG. 1 depicts a diagram of telecommunications system 100 in the priorart. Telecommunications system 100 comprises wireless telecommunicationsterminals 101-1 through 101-L, wherein L is a positive integer that isequal to five in the example depicted; access point 103 that servesbasic service area 110; and telecommunications network 120, all of whichare interconnected as shown.

Basic service area 110 is the service area in which shared access toother nodes in telecommunications system 100 is provided totelecommunications terminals such as terminals 101-1 through 101-L. Asdepicted in FIG. 1, basic service area 110 is in an IEEE 802.11 wirelesslocal area network. In area 110, the one or more wirelesstelecommunications terminals that make up the basic service set of area110 are able to access other nodes in system 100 via ashared-communications channel supported by access point 103.

Telecommunications network 120 is a telecommunications network such asthe Internet, the Public Switched Telephone Network (PSTN), and soforth. Network 120 comprises or is connected to one or moretransmission-related nodes such as gateways, routers, or switches thatare used to direct packets from one or more sources to the correctdestinations of those packets.

The service provided by the path that links a first node with a secondnode is characterized by its “quality of service.” Quality of service,for the purposes of this specification, is defined as, from one node toanother, a function of the (i) bandwidth, which can be expressed inunits such as bits per second, (ii) error rate, which can be expressedin units such as bit errors per number of bits transmitted, and (iii)latency, which can be expressed in units such as seconds. For example, ashared-communications channel that links a wireless terminal such asterminal 101-1 with an access point such as access point 103 is subjectto a quality-of-service level.

Each of telecommunications terminals 101-l, for l=1 through L, is acommunications device such as a local area network telephone, a notebookcomputer, a personal digital assistant (PDA), a tablet PC, and so forth.Terminals 101-1 through 101-L are assigned fixed Internet Protocoladdresses and, as wireless stations, are assigned Internet Protocoladdresses from a pre-specified block of addresses. Terminals 101-1through 101-L communicate, through access point 103, with othertelecommunications terminals that have connectivity with network 120. Inorder to communicate, a user at a first telecommunications terminal insystem 100, such as terminal 101-1, places a “call” (e.g., voice call,email, text chat, video, etc.) to a user at a second terminal in system100.

Each telecommunications terminal may use a “codec,” as is known in theart, to more efficiently transmit user information, such as voicesignals, by compressing the transmitted information and decompressingthe received information. A codec has an associated “codec rate” thatspecifies how much (compressed) information actually has to betransmitted per unit time.

System 100 has to be able to determine whether to admit each call. Calladmission control is necessary, considering that terminal 101-1 is alsocompeting with other terminals in its basic service area (i.e., area110) for the shared-communications channel provided by access point 103.In fact, access point 103 has to be able to handle multiple trafficstreams-each stream comprising a series of packets-that are transmittedto or from wireless terminals via the correspondingshared-communications channel.

Furthermore, each terminal has an associated level of mobility. Aterminal that is immobile (i.e., is fixed) is able to support a maximumdata rate that is more-or-less constant. In contrast, as amobility-capable terminal moves closer to or away from its access point,the maximum data rate at which the terminal is able to communicate withthe access point changes during a call. When the terminal is close tothe access point, the signal is generally stronger and, as a result, themaximum data rate is higher. Likewise, when the terminal is far from theaccess point, the signal is generally weaker and, as a result, themaximum data rate is lower. As a result, the actualshared-communications channel bandwidth that the terminal utilizes-thatis, the channel occupancy used by the terminal-during a call changesover time. Furthermore, there can be multiple terminals using theshared-communications channel for calls, where each terminal is able tomove independently of one another during a call.

In some techniques in the prior art, the spatial distribution of thedifferent terminals within the basic service area might be consideredduring the call admission process. This is advantageous in that itconsiders the data rates for the actual shared-communications channel,instead of merely using data rates from an analytical model of the basicservice area. However, this is disadvantageous in that the terminals,being at different distances from the access point, have differentsupported data rates, which can cause the call admission criterion tohave greater variance and lower the utilized bandwidth. As a consequencein some cases, the net effect is to allow fewer calls.

SUMMARY OF THE INVENTION

The present invention is a technique to optimize the call admissioncontrol algorithm that governs a shared-communications channel, in whichthe algorithm accounts for the levels of mobility, on an individualbasis, of one or more terminals that need to use the channel. Instead ofdetermining the variation in the distribution of supported data ratesaggregated across multiple terminals—which can result in a greatervariance in the call admission criterion—the technique of theillustrative embodiment tracks the variation in the distribution, foreach terminal, of the data rates for that terminal. In short, thetechnique of the illustrative embodiment accounts for the variance indata rates that is attributed to the mobility of individual,representative terminals and not to the variance that is attributed tothe spatial distribution of multiple terminals.

Conceptually, each monitored terminal that uses a particularshared-communications channel has an associated “probability oftransition” that is related to the terminal's level of mobility, inwhich the probability of transition refers to the likelihood that theterminal's supported data rate will increase or decrease, relative tothe current supported data rate. The probability of transition of aparticular terminal is at or near zero if the terminal is immobile, suchas a personal computer being used at a desk. On the other hand, theprobability of transition of another terminal is high if that terminalis moving around the basic service area, as in the case of a userwalking with a WiFi-enabled handset. In accordance with the illustrativeembodiment of the present invention, the probabilities of transitionsfor a representative set of terminals are, in essence, accounted for indetermining the channel occupancy for a set of simultaneous calls. As aresult, by using the technique of the illustrative embodiment, ashared-communications channel that serves various mobility mixes ofterminals is able to handle more calls simultaneously because thevariation in the distribution of the data rate measurements that is usedin the call admission criterion is often less than it is with sometechniques in the prior art.

In accordance with the illustrative embodiment of the present invention,a channel utilization manager accounts for the probabilistic nature ofthe call admission decision by using a continually-refined value torepresent the channel occupancy. The “per-call” channel occupancy valueis determined by a number of factors, including the levels of mobilitythat are associated with the various telecommunications terminals. Theper-call channel occupancy for a given level of mobility andshared-communications channel data rate is updated through empiricalobservation, and is used in the manner described below.

In accordance with the illustrative embodiment, channel occupancy isincorporated into one or more cumulative distribution functions (CDF) ofchannel occupancy. For a given shared-communications channel, eachchannel occupancy CDF represents the probability of a given channeloccupancy level, while taking into account the number of calls (e.g., 1call, 2 calls, etc.) and other parameters that include (i) thevariability in the maximum data rates of the terminals present, (ii) thelevels of mobility being experienced in the coverage area, and (iii) theapplication of different data-transmission requirements (e.g., codecrate, etc.) to each of those terminals when on a call.

The channel utilization manager is able to refine the channel occupancyvalues during the processing of live calls on a shared-communicationschannel. The access point that supports the channel regularly reports tothe manager the data rate supported by a terminal, for multipleterminals that are monitored. In accordance with the illustrativeembodiment, for each terminal, the level of mobility is updated byrecalculating a measure of the variation in the distribution ofsupported data rates for the particular terminal; the channeloccupancies are, in turn, are updated by factoring in the level ofmobility of one or more terminals.

When the channel utilization manager considers admitting a candidatecall and that call would be the Nth concurrent call on theshared-communications channel, the manager evaluates channel occupancyby using the N-call CDF for the mix of mobility levels employed by theestablished calls and the new call. For example, one five-call CDF mightbe for 2 fixed calls and 3 mobile calls, while another five-call CDFmight be for 4 fixed calls and 1 mobile call. The evaluation determineswhether the resulting channel occupancy would be less than or equal toan adjustable bandwidth threshold (e.g., 80 percent of the channel'slimit, etc.), at a probability that exceeds confidence level (e.g., 98%,etc.). If this admission criterion is met, the channel utilizationmanager admits the call, in accordance with the illustrative embodimentof the present invention.

Although the utilization management in the illustrative embodiment isapplied to the managing of a shared-communications channel, the presentinvention can be applied to managing other types of resources that areshared by users, as those who are skilled in the art will appreciate.

The illustrative embodiment of the present invention comprises:receiving i) a plurality of data rate measurements, wherein the datarate measurements in the plurality are of the physical layer data ratesthat are supported over a shared-communications channel by one or moretelecommunications terminals, and ii) a data-transmission requirementfor a call that is to involve a first telecommunications terminal,wherein the first telecommunications terminal has transmitted at leastpart of the data-transmission requirement via the shared-communicationschannel; calculating a first measure of the variation in thedistribution of a first set of data rate measurements taken from theplurality, wherein the data rate measurements in the first set are for asingle telecommunications terminal; and determining whether to admit thecall on the shared-communications channel, based on (i) the firstmeasure and (ii) the data-transmission requirement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a diagram of telecommunications system 100 in the priorart.

FIG. 2 depicts a diagram of telecommunications system 200 in accordancewith the illustrative embodiment of the present invention.

FIG. 3 depicts the salient components of channel utilization manager 207in accordance with the illustrative embodiment of the present invention.

FIG. 4 depicts an illustrative series of messages that are exchangedbetween (i) access point 203 and (ii) channel utilization manager 207during the course of managing terminal 201-1.

FIG. 5 depicts a diagram of the message flow associated with an exampleof the user of telecommunications terminal 201-1 calling a user attelecommunications terminal 206.

FIG. 6 depicts a flowchart of the salient tasks associated with channelutilization manager 207 determining whether to admit a call, inaccordance with the illustrative embodiment of the present invention.

FIG. 7 depicts a set of cumulative distribution functions of channeloccupancy for varying numbers of calls.

FIG. 8 depicts a flowchart of the salient tasks associated with channelutilization manager 207 updating one or more channel occupancydistribution functions, in accordance with the illustrative embodimentof the present invention.

FIG. 9 depicts a set of cumulative distribution functions of channeloccupancy for varying mixes of mobility present.

DETAILED DESCRIPTION

The following terms are defined for use in this Specification, includingthe appended claims:

-   -   The term “data-transmission requirement,” and its inflected        forms, is defined as a requirement for the proper transmission        of data, wherein the data transmission occurs via a        communications resource, such as a wireless        shared-communications channel. Examples of data-transmission        requirements include the data periodicity to be maintained,        quality-of-service requirements (i.e., related to bandwidth        required, maximum error rate, and maximum latency), and so        forth. The required bandwidth refers to the data rate, or the        channel time, that is required for the traffic stream of data to        be transmitted.    -   The term “traffic stream description,” and its inflected forms,        is defined as the information that specifies the        data-transmission requirements, either explicitly or implicitly.        For example, instead of explicitly stating a requirement (e.g.,        data rate of 1 Mbps, etc.), the traffic stream description might        identify the codec, as is known in the art, to be used by a        wireless terminal during a call, wherein the particular choice        of codec implies a certain bandwidth requirement for the call. A        telecommunications terminal that is preparing to communicate        data originates the traffic stream description.

The term “call,” and its inflected forms, is defined as a communicationof user information between two or more telecommunications terminals.Examples of a call are a voice telephone call, an email, a text-basedinstant message [IM] session, a video conference, etc.

FIG. 2 depicts a diagram of telecommunications system 200 in accordancewith the illustrative embodiment of the present invention.Telecommunications system 200 comprises wireless telecommunicationsterminals 201-1 through 201-M, wherein M is a positive integer that is,in the illustrative embodiment, equal to five; access point 203 thatserves basic service area 210; server 205; telecommunications terminal206; channel utilization manager 207; and telecommunications network220, interconnected as shown.

Telecommunications system 200 is capable of Session InitiationProtocol-based (SIP-based) signaling, in accordance with theillustrative embodiment. It will be clear to those who are skilled inthe art, however, how to apply the present invention to some alternativeembodiments that use other types of call-control signaling, such asH.323, as is known in the art.

Basic service area 210 is in a telecommunications network that providesshared access of other nodes in telecommunications system 200 totelecommunications terminals such as terminals 201-1 through 201-M. Asdepicted in FIG. 2, area 210 is in an IEEE 802.11 wireless local areanetwork, in accordance with the illustrative embodiment. As those whoare skilled in the art will appreciate, however, area 210 in somealternative embodiments can be in another type of shared-access network,such as an Ethernet network or cable modem-based network, either wiredor wireless. In area 210, shared access is provided to one or morewireless telecommunications terminals via a shared-communicationschannel that is supported by corresponding access point 203.

Telecommunications network 220 is a telecommunications network such asthe Internet, the Public Switched Telephone Network (PSTN), and soforth. Network 220 comprises or is connected to one or moretransmission-related nodes such as gateways, routers, or switches thatare used to direct packets from one or more sources to the correctdestinations of those packets.

Each of telecommunications terminals 201-m, for m=1 through M, as wellas terminal 206, is a communications device such as a local area networktelephone, a notebook computer, a personal digital assistant (PDA), atablet PC, and so forth, and has a contact identifier. Terminals 201-1through 201-M are assigned fixed Internet Protocol addresses and, aswireless stations, are assigned Internet Protocol addresses from apre-specified block of addresses. Terminals 201-1 through 201-Mcommunicate, through access point 203, with other telecommunicationsterminals that have connectivity with network 220, such as terminal 206.For example, terminal 201-m is associated with access point 203 asdepicted in FIG. 2 and uses the corresponding shared-communicationschannel to communicate wirelessly with other devices. In order tocommunicate, a user at a first telecommunications terminal in system200, such as terminal 201-1, places a “call” (e.g., voice call, email,text chat, video, etc.) to a user at a second terminal in system 200,such as terminal 206. Terminals 201-1 through 201-M are also capable ofcommunicating with one another with the attendant call control signalingbeing routed through one or more nodes connected to network 220, asdescribed below.

Terminals 201-1 through 201-M are capable of varying levels of mobility,with respect to one another. Each terminal 201-m's level of mobility ata particular moment is determined by the terminal's design or use, orboth. For example, terminal 201-1 might be a WiFi handset that its usercan carry around while talking, in which case terminal 201-1 has highlevel of mobility associated with it, at least while it is moving. Incontrast, terminal 201-2 might be a notebook computer parked on a desk,in which case terminal 201-2 has a low level of mobility associated withit.

It will be clear to those skilled in the art how to make and useterminals 201-1 through 201-M and terminal 206.

Access point 203 is an access point as is known in the art thatexchanges packets that convey data (e.g., control messages, voicetraffic, video streams, etc.) with one or more wirelesstelecommunications terminals, such as terminal 201-m, via itsshared-communications channel. Access point 203, in well-known fashion,employs a contention-based protocol (e.g., IEEE 802.11 DCF, etc.) forensuring that a wireless terminal or access point can gain exclusiveaccess to the shared-communications channel for an interval of time inorder to transmit packets.

Access point 203 also has to be able to handle traffic streams, each ofwhich comprising a series of packets, that are transmitted to or fromwireless terminals via the shared-communications channel. In accordancewith the illustrative embodiment, access point 203 is capable ofhandling the requests from an associated wireless terminal to admit sucha traffic stream. It will be clear to those skilled in the art how tomake and use access point 203.

Server 205 is a Session Initiation Protocol (SIP) proxy server, as isknown in the art. In accordance with the illustrative embodiment of thepresent invention, server 205 also transmits information to channelutilization manager 207 to determine whether a call should be allowed ona shared-communications channel. How server 205 interacts with othernodes in setting up and managing calls is described below and withrespect to FIGS. 4 through 9.

As those who are skilled in the art will appreciate, in some alternativeembodiments, server 205 can be a different type of server such asanother type of SIP server or another type of call-control server thatuses a different protocol (e.g., H.323, etc.). In any event, it will beclear to those skilled in the art, after reading this specification, howto make and use server 205.

In accordance with the illustrative embodiment, channel utilizationmanager 207 provides the admission control to handle requests to addtraffic streams that utilize the shared-communications channels of oneor more access points, including access point 203. The salientcomponents of manager 207 are described below and with respect to FIG.3. If, for example, the channel utilization of a particularshared-communications channel exceeds a predetermined level, manager 207may disallow a new call on that channel.

Manager 207 is able to receive the following information from thespecified nodes:

-   -   i. a registration, from an access point such as access point        203;    -   ii. a notification that a terminal has associated with an access        point such as access point 203;    -   iii. a message that contains the physical data rate that is        supported by a terminal active in a call (i.e., the supported        data rate), where the message can be sent repeatedly to update        the supported data rate;    -   iv. a notification that a terminal has disassociated from an        access point such as access point 203;    -   v. a measurement of the shared-communications channel quality        (e.g., noise, collision rate, frame or bit error rate, etc.),        from an access point such as access point 203;    -   vi. the bandwidth that is committed through IEEE 802.11e traffic        specifications (TSPEC), as are known in the art, to traffic        streams that do not involve server 205 (e.g., direct link        protocol [DLP] transmissions, etc.);    -   vii. a resource reservation request for a particular call, from        server 205; and    -   viii. a notification of the ending of a particular call, from        server 205.        In addition, manager 207 is able to transmit the following        information to the specified nodes:    -   i. a resource reservation response for a particular call, to        server 205; and    -   ii. a notification that an existing call is being rejected, to        server 205.

How manager 207 interacts with access point 203 and server 205 inadmitting and enabling calls is described below and with respect toFIGS. 4 through 9. It will be clear to those skilled in the art, afterreading this specification, how to make and use manager 207.

FIG. 3 depicts the salient components of channel utilization manager 207in accordance with the illustrative embodiment of the present invention.Manager 207 comprises network interface 301, processor 302, and memory303, interconnected as shown.

Network interface 301 receives signals from other nodes via network 220and forwards the information encoded in the signals to processor 302, inwell-known fashion. Network interface also receives information fromprocessor 302 and transmits signals that encode this information toother nodes via network 220, in well-known fashion. It will be clear tothose skilled in the art, after reading this specification, how to makeand use network interface 301.

Processor 302 is a general-purpose processor that is capable ofreceiving information from network interface 301, executing instructionsstored in memory 303, reading data from and writing data into memory303, executing the tasks described below and with respect to FIGS. 4through 9, and transmitting information to network interface 301. Insome alternative embodiments of the present invention, processor 302might be a special-purpose processor. In either case, it will be clearto those skilled in the art, after reading this specification, how tomake and use processor 302.

Memory 303 stores the instructions and data used by processor 302.Memory 303 might be any combination of random-access memory (RAM), flashmemory, disk drive memory, and so forth. It will be clear to thoseskilled in the art, after reading this specification, how to make anduse memory 303.

FIG. 4 depicts an illustrative series of messages that are exchangedbetween (i) access point 203 and (ii) channel utilization manager 207during the course of managing terminal 201-1, in accordance with theillustrative embodiment of the present invention. Although interactionwith a single terminal is depicted, as those who are skilled in the artwill appreciate, access point 203 and manager 207 are able to handleinformation exchanges with multiple terminals concurrently. As those whoare skilled in the art will appreciate, some of the messages that aredepicted in FIG. 4 can be transmitted or received in a different orderthan that depicted.

When an access point initializes, it registers with channel utilizationmanager 207. As depicted in FIG. 4, access point 203 transmitsregistration message 401 to manager 207. The registration message fromthe access point identifies the capability of the physical layer of theshared-communications channel (e.g., IEEE 802.11a-capable, IEEE802.11g-capable, etc.) to manager 207, which uses the information todetermine the physical layer data rate of the particularshared-communications channel. The registration message also reportsenvironmental parameters that affect capacity, including backgroundnoise, transmission attempt failure rate, and so forth; the access pointmay also transmit a registration message when an environmentalparameter, such as background noise, changes. Furthermore, if there areIEEE 802.11e traffic specifications that are admitted by access point203 without server 205 being involved, the access point reports tomanager 207 the total bandwidth committed to all the terminals in thecorresponding basic service area (i.e., area 210).

When a telecommunications terminal associates with an access point, theaccess point updates manager 207. As depicted in FIG. 4, terminal 201-1for example associates with access point 203 by transmitting message402; access point 203 indicates this to manager 207 by transmittingmessage 403, which comprises the Internet Protocol address and physicallayer capabilities of terminal 201-1, including the terminal's physicallayer data rate. The access point may also transmit message 403 when thephysical layer data rate of the terminal changes, which may occur when,for example, the terminal moves closer to or away from the access pointand supports a different maximum data rate than before.

Meanwhile, in some embodiments, access point 203 continually updatesmanager 207 on the quality of its shared-communications channel orcommitted bandwidth, or both, by transmitting message 404 eitherperiodically or sporadically.

As depicted in FIG. 4, at some point terminal 201-1 disassociates withaccess point 203 via message 405, in well-known fashion. Accordingly,access point 203-1 transmits message 406 in response to disassociationmessage 405. Alternatively, a terminal may dissociate from access point203 without sending a message; in this case, inactivity, as determinedby the access point, triggers disassociation and causes the access pointto update manager 207 about the disassociation.

FIG. 5 depicts a message flow diagram that is related to handling callsbetween two telecommunications terminals, in which at least one of theterminals uses a shared-communications channel. In accordance with theillustrative embodiment, some or all of the message flow described aboveand with respect to FIG. 4 may occur concurrently with the message flowdepicted in FIG. 5; for example, channel utilization manager 207continually receives message 404 that reports channel quality fromaccess point 203. Manager 207 might also repeatedly receive a messagesuch as message 403, which can report a terminal's physical layer datarate as received by the access point. As those who are skilled in theart will appreciate, some of the messages that appear in FIG. 5 can betransmitted or received in a different order than the order depicted.

FIG. 5 depicts a diagram of the message flow associated with an exampleof the user of telecommunications terminal 201-1 calling a user attelecommunications terminal 206, in accordance with the illustrativeembodiment of the present invention, wherein channel utilization manager207 accepts the call. Terminal 201-l's user initiates the message flowby entering a command into terminal 201-1 to place a call to the otheruser. Terminal 201-1 transmits message 501, a SIP INVITE message, toserver 205. Message 501 comprises (i) a traffic stream description(e.g., a SIP Real-Time Protocol [RTP] payload type, etc.) that specifiesthe nature of the call and (ii) the user identifier of the person beingcalled. The traffic stream description also includes one or moredata-transmission requirements (e.g., required bandwidth, etc.), as partof a media description for the candidate call.

Server 205 determines which terminal is currently associated with theuser identifier of the called user (i.e., the “destination terminal”),and transmits message 502, a SIP OPTIONS message, to the destinationterminal, in this case terminal 206, to determine the capabilities ofthat terminal (e.g., whether the destination terminal supports certaintypes of media, etc.). Server 205 also determines, in well-knownfashion, from the calling terminal's Internet Protocol address that theserver should remain on the signaling path that was used to receive theSIP INVITE message. Telecommunications system 200 uses the Record-Routeheader mechanism, as is well-known in the art, to indicate to server 205that it will be a “call-stateful” proxy for the call. Accordingly,server 205 remains on the signaling path for at least part of the call,if admitted, in accordance with the illustrative embodiment.

Server 205 also transmits response message 503, a SIP TRYING message,back to wireless terminal 201-1, indicating that the server isattempting to set up the call.

Destination terminal 206 transmits message 504 to server 205 (e.g., aSIP OK message, etc.) in response to message 502.

Server 205 determines that terminal 201-1 is wireless and is served byan access point that is managed by channel utilization manager 207(i.e., access point 203), and that manager 207 has to therefore benotified of the candidate call. Server 205 determines terminal 201-1'saccess method by checking terminal 201-1's Internet Protocol addressagainst a list of addresses that correspond to terminals associated withwireless local area networks. As those who are skilled in the art willappreciate, server 205 can determine terminal 201-1's access methodthrough other means in some alternative embodiments.

Subsequently, server 205 transmits message 505 to manager 207. Message505 is a call-setup traffic specification, which comprises an admissionrequest with a description of the traffic stream with one or moredata-transmission requirements (e.g., periodicity, required data rate,etc.).

Channel utilization manager 207 receives message 505 from server 205 andstores the received call-setup traffic specification in a newly createdrecord associated with the call. Manager 207 then determines whether itshould admit the call on the shared-communications channel, inaccordance with the illustrative embodiment of the present invention, asdescribed below and with respect to FIGS. 6 through 9.

In the illustrative message flow depicted in FIG. 5, manager 207determines that the candidate call is to be admitted. As a result,manager 207 (i) notes the additional call and the accompanyingutilization in its database (i.e., sets or otherwise changes the valueof a flag that signifies call admittance), and (ii) transmits acceptancemessage 506 to server 205, indicating that the candidate call isadmitted.

Server 205 then transmits message 507, a SIP INVITE message, todestination terminal 206. Subsequently, server 205 continues to set upthe call between terminals 201-1 and 206 in well-known fashion.

As those who are skilled in the art will appreciate, manager 207 mightdetermine that a call is not to be admitted and, as a result, cantransmit a message to server 205, indicating that the manager hasrejected the call.

As those who are skilled in the art will further appreciate, manager 207can handle the scenario in which terminal 201-1 moves from access point203's coverage area to another access point's coverage area. In otherwords, system 200 is capable of performing a “handover” of terminal201-1 from one access point to another. In some embodiments, manager 207places a greater emphasis on admitting handover-related calls on ashared-communications channel than new calls. In those embodiments, inorder to effectively reserve channel resources for handover-relatedcalls, manager 207 rejects new calls at a lower utilization level thanthat of handover calls. Nevertheless, if the utilization level exceedsthe level at which handover calls are to be rejected, manager 207transmits a message to server 205 that indicates to the server that theexisting call is unacceptable and that it should drop the call.

In some alternative embodiments, handover-related calls are admittedunconditionally or are admitted if they are of a specified prioritylevel (e.g., E911 calls, etc.). If overall quality-of-service on theutilized shared-communications channel deteriorates, manager 207 candrop other calls or further lower the utilization level at which newcalls are rejected.

FIG. 6 depicts a flowchart of the salient tasks associated with channelutilization manager 207 determining whether to admit a call onto theshared-communications channel served by access point 203, in accordancewith the illustrative embodiment of the present invention. In theexample provided, terminal 201-1 is involved in the call that manager207 is considering. As those who are skilled in the art will appreciate,some of the tasks that appear in FIG. 6 can be executed in a differentorder than the order depicted.

General Explanation —As terminal 201-1 moves closer to or away fromaccess point 203, the terminal can change the actual data rate that ituses to communicate; consequently, the actual bandwidth that is utilizedby the corresponding call changes.

In accordance with the illustrative embodiment, channel occupancy isincorporated into one or more cumulative distribution functions (CDF) ofchannel occupancy, the characteristics of which are determined, at leastin part, by the levels of mobility that are associated with one or moreof terminals 201-1 through 201-M. For a given shared-communicationschannel, each channel occupancy CDF represents the probability of agiven channel occupancy level, while taking into account the number ofcalls (e.g., 1 call, 2 calls, etc.) and other parameters that includethe variability in the maximum data rates of the terminals present. Theprobability distributions for 1 call, 2 calls, 3 calls, and so forth maybe calculated either ahead of time or while processing the calladmission decision to account for, while not being limited to, thefollowing parameters:

-   -   i. each shared-communications channel physical layer rate        supported (e.g., 54 Mbps, 11 Mbps, etc.);    -   ii. the probability that a given terminal will be served at a        given physical layer rate;    -   iii. each quality-of-service criterion to be considered (e.g.,        10 ms maximum delay, 50 ms maximum delay, etc.);    -   iv. the data-transmission requirements for the call, including        the codec to be used; and    -   v. the probability of transition from one physical layer rate to        another for each represented terminal.

When channel utilization manager 207 considers admitting a candidatecall and that call would be the Nth concurrent call on theshared-communications channel, the manager evaluates the N-call CDF todetermine whether the resulting channel occupancy would be less than orequal to an adjustable bandwidth threshold (e.g., 80 percent of thechannel's limit, etc.), at a probability that exceeds the desiredconfidence level (e.g., 98%, etc.). If this admission criterion is met,channel utilization manager 207 admits the call, in accordance with theillustrative embodiment of the present invention.

In accordance with the illustrative embodiment, each channel-occupancyCDF of a shared-communications channel is generated from a distributionfunction (e.g., a probability distribution function [PDF], etc.) of theterminals' data rates on that channel. A probability distribution of theterminals' data rates is generated from analytical models or fromongoing data rate information received from an access point, or both.Estimating the data rate probability distribution provides an efficientway to derive a channel occupancy probability distribution for a varietyof combinations of codec type and number of calls.

Channel utilization manager 207 is able to refine the channel occupancyvalues during the processing of live calls on a shared-communicationschannel. The access point that supports the channel (e.g., access point203-1, etc.) regularly reports to manager 207 the data rate supported bya terminal, for multiple terminals. An empirically derived probabilitydistribution, as such, reflects both the propagation environment and thespatial distribution of the terminals that are involved in calls in thebasic service area. Thus, the probability distribution and calladmission criterion are tailored to the particular basic service areamonitored and supported by the access point.

Channel utilization manager 207 initially accounts for the probabilisticnature of the call admission decision by using a pre-determined,statistically justified value to represent the channel occupancy. The“per-call” channel occupancy value is determined by a number of factors,including the shared-communications channel data rate. The initialper-call channel occupancy for a given codec and shared-communicationschannel data rate is determined through empirical observation or throughsimulation models, and is used in the manner described below.

In accordance with the illustrative embodiment of the present invention,channel utilization manager 207 subsequently accounts for theprobabilistic nature of the call admission decision attributable tomobility by using measurements of the supported data rate that manager207 receives during the course of a call from a terminal, for one ormore terminals, in the manner described below. Mobility is taken intoaccount because those terminals with low or no mobility result in a CDFwith a one set of characteristics (e.g., slope, point or range at whichsteepest slope occurs, etc.), while terminals with moderate mobilityresult in a CDF with another set of characteristics, while terminalswith high mobility result in a CDF with still another set ofcharacteristics.

Described Tasks—At task 601, manager 207 generates an initial data ratedistribution function of telecommunications terminal data rates. At thestart of the process, manager 207 receives the maximum physical layerrate of the shared-communications channel (e.g., via message 401, etc.)from the corresponding access point, such as access point 203. In someembodiments, manager 207 then uses known environmental conditions suchas the applicable path loss and background noise level to estimatemaximum data rates available at various distances from the access point,given the received maximum data rate of the channel. In this analyticalmodel, manager 207 proceeds to estimate a hypothetical terminal'sprobability of being at various places in the coverage area of theshared-communications channel and, therefore, the probability ofoperating at various data rates. From this data, manager 207 thengenerates a data rate distribution function in well-known fashion.

At task 602, manager 207 generates one or more channel occupancycumulative distribution functions (CDF), in accordance with theillustrative embodiment, wherein the channel occupancy CDFs are based onthe data rate distribution function generated at task 601. Anillustrative set of channel occupancy CDFs is depicted in FIG. 7, inwhich the CDFs are graphically represented. As explained earlier, eachof the channel occupancy CDFs accounts for a different number of calls,as well as different mixes of other parameters, such as codec rates. Ina simplified scenario, however, in which the same data-transmissionrequirements apply for all calls (e.g., the same codec rate, etc.), itis possible to have exactly one channel occupancy CDF per each differentvalue in the number of calls to be considered. For example, for amoderate level of mobility that is associated with area 210, curve 701represents the CDF for 19 simultaneous calls, curve 702 represents theCDF for 20 simultaneous calls, and curve 703 represents the CDF for 21simultaneous calls, in which all of the calls have the samedata-transmission requirements.

In accordance with the illustrative embodiment, the channel occupancyCDFs are based, at least in part, on the levels of mobility of one ormore terminals. The channel occupancy CDFs that are initially generatedcan incorporate an assumed or default level of mobility, such as themoderate level of mobility associated with the distribution functionsdepicted in FIG. 7. Subsequently, the levels of mobility that areassociated with a shared-communications channel can be monitored andupdated, as described below and with respect to FIG. 8.

As those who are skilled in the art will appreciate, in some embodimentsthe channel occupancy CDFs are generated without involving manager 207,while in some other embodiments some or all of the values are generatedby manager 207. It should be obvious to those skilled in the art thatwhen making a call admission decision, given that a mix of differentcodecs is used by the N calls, it is not necessary to generate theentire CDF of channel occupancy by N calls. It is sufficient to computethe probability that channel occupancy will not exceed the specifiedthreshold level. If that probability is greater than or equal to thedesired confidence level, the Nth call is admitted.

At task 603, manager 207 receives a data-transmission requirement for acandidate call. The requirement, for example, can be a specified codectype and rate.

At task 604, manager 207 adjusts a confidence level, T, that will beused in the call admission process. In some embodiments, the value of Tis based on whether the candidate call is a new call or a call beinghanded over from another shared-communications channel (i.e., anexisting call). In some alternative embodiments, the value of T isunaffected by the type of call being considered. In some otheralternative embodiments, the value of the parameter BW is based onwhether the candidate call is a new or existing call.

At task 605, manager 207 evaluates the following inequality:

Probability [channel occupancy≦BW|calls_description]>T,

where BW is the fraction (e.g., 0.8, etc.) that can be allocated tocalls of the total shared-communications channel, T is the confidencelevel, and calls_description refers to one or more parameters thatdescribe the mix of calls, including:

-   -   i. N, which is the number of calls that would be concurrently        using the shared-communications channel,    -   ii. QoS_(MIN), which refers to the minimum quality of service        that is allowed throughout all calls present (e.g., delay less        than 5 milliseconds, etc.), and    -   iii. level of mobility, which refers to the level or levels of        mobility associated with the shared-communications channel, and        which is described below and with respect to FIG. 8.        The probability distribution used is the channel occupancy CDF        for N number of calls. If the inequality is true, then the call        can be admitted and task execution proceeds to task 606. If the        inequality is false, then the call cannot be admitted and task        execution proceeds to task 607. As those who are skilled in the        art will appreciate, a different inequality or criteria can be        used to assess whether a candidate call should be admitted or        not.

At task 606, manager 207 admits the call and notifies otherdata-processing systems accordingly. Task execution then proceeds totask 608.

At task 607, manager 207 denies the call and notifies otherdata-processing systems accordingly.

At task 608, manager 207 checks if there are any shared-communicationschannel-related parameters that are being received. If there are, taskexecution proceeds to task 609. If not, task execution proceeds to task603.

At task 609, manager 207 receives the current supported data rates ofone or more of terminals 201-1 through 201-M via access point 203.

At task 610, manager 207 updates the data rate distribution functionbased on the data rates received at task 609. Over time, the mobilitypatterns of terminals in the actual operating environment influence thedata rate distribution function that was initially generated based onassumptions. In this way, the data rate distribution function is updatedto reflect the operating environment of basic service area 210 supportedby access point 203.

At task 611, manager 207 receives, from access point 203, achannel-quality measurement (e.g., background noise, collision rate,etc.) of the shared-communications channel or a channel utilizationmeasurement. For example, manager 207 might receive the information fromaccess point 203 via message 405. The channel quality measurements aredescribed above and with respect to FIG. 4.

At task 612, manager 207 optionally updates the BW parameter based onthe parameters received at task 611. In this way, manager 207 considersthe presence channel impairments (e.g., noise, etc.) and other trafficon the shared-communications channel, and their effects on the actualusable bandwidth of the channel. Task execution then proceeds to task602. Manager 207, in some other embodiments, may also adjust the usablebandwidth by considering the bandwidth that is committed through IEEE802.11e traffic specifications to traffic streams that do not involveserver 205.

FIG. 8 depicts a flowchart of the salient subtasks associated withchannel utilization manager 207 executing task 602, in which manager 207updates the channel occupancy cumulative distribution function, inaccordance with the illustrative embodiment of the present invention. Asthose who are skilled in the art will appreciate, some of the tasks thatappear in FIG. 8 can be executed in a different order than the orderdepicted.

At task 801, manager 207 initializes the telecommunications terminalcounter, m.

At task 802, manager 207 checks if a supported data rate has beenreceived for terminal 201-m. If one has been received, task executionproceeds to task 803. If not, task execution proceeds to task 804.

At task 803, manager 207 calculates a measure of the variation in thedistribution of a set of data rate measurements for terminal 201-m, inaccordance with the illustrative embodiment. This measure represents theprobability of transition to a different supported data rate from thecurrent rate for a particular terminal. For each terminal, manager 207determines and maintains the measure of the variation by tracking thedistribution of two or more received data rates that were experiencedduring a particular call, or even across multiple calls, involving thatparticular terminal on the particular shared-communications channel. Insome embodiments, the measure that is calculated is the statisticalvariance of the data rate relative to the mean, while in some otherembodiments the measure is the standard deviation.

At task 804, manager 207 determines a level of mobility for terminal201-m, based on one or more characteristics that include, but are notlimited to (i) the measure of the variation and (ii) a data-transmissionrequirement. For example, manager 207 can infer the level of mobility ofa telecommunications terminal by using the codec specified in thedata-transmission requirement by the terminal. In the example, a firsttype of codec might typically be associated with low-mobilityapplications, while a second type of codec might typically be associatedwith high-mobility applications.

At task 805, manager 207 increments the terminal counter, m.

At task 806, manager 207 determines whether the probabilities oftransition for all of the terminals being monitored have been consideredand updated when necessary. If so, task execution proceeds to task 807.If not, task execution proceeds to task 802.

At task 807, manager 207 updates the channel occupancy cumulativedistribution function (CDF) for the shared-communications channelassociated with basic service area 210, based on the levels of mobilityof one or more telecommunications terminals, and on the data ratedistribution function of the shared-communications channel. Taskexecution then proceeds to task 603.

An illustrative set of updated channel occupancy CDFs is depicted inFIG. 9, in which the CDFs are graphically represented. Each of thechannel occupancy CDFs accounts for a different level of mobility for agiven number of calls, in this case twenty calls. For example, curve 901represents the channel occupancy CDF for 19 calls from low-mobilityterminals and 1 call from a high-mobility terminal. Curve 902 representsthe channel occupancy CDF for 10 calls from low-mobility terminals and10 calls from high-mobility terminals. Curve 903 represents the channeloccupancy CDF for 1 call from a low-mobility terminal and 19 calls fromhigh-mobility terminals. For pedagogical purposes, all of the twentycalls represented in each CDF are subject to the same data-transmissionrequirements and fit within the categories of “low-mobility” and“high-mobility”; however, it will be clear to those skilled in the art,after reading this specification, how to generate and use CDFs toaccount for differing data-transmission requirements and for a differentset of mobility categories than that depicted.

Because a basic service area that typically serves a low-mobility mix ofterminals has a lower overall variation in the data rate distributionthan that of an area with a high-mobility mix, the low-mobility area isable to handle more calls, as reflected in the CDFs and as the result ofthe technique of the illustrative embodiment. As those who are skilledin the art will appreciate, the actual characteristics of each CDF canbe different than that depicted for the various mobility mixesrepresented, and the depicted curves are mainly intended to illustratethat different channel occupancy CDFs can result from different levelsof mobility, leading to a more optimized call admission control.

To illustrate the technique of the illustrative embodiment, threeexamples are presented here, in which each example comprises a differentmobility mix of terminals. In the first example, all of the terminals inthe mix are highly mobile, such as in a building's main corridor inwhich the terminal users are continually moving. In the second example,roughly half of the terminals are highly mobile, while half of theterminals hardly move (or are immobile) during calls, such as in aconference area where some users are sitting and some are walkingaround. In the third example, all of the terminals in the mix are of lowmobility, such as in an office area, in which the users are sittingdown.

In each example, a measure of the variation of the data ratedistribution is maintained for each terminal monitored. In accordancewith the illustrative embodiment, multiple measurements of the supporteddata rate are accumulated for one or more calls that involve a monitoredterminal. In the high-mobility mix, the variation for each terminalindicates that the data rate varies significantly, which indicates thatthe terminals are highly mobile. In the moderate-mobility mix, themeasure of variation for some of the terminals is large, implying highmobility, while the measure for other terminals is small, indicating lowor no mobility. In the low-mobility mix, the variation for each terminalis close to zero, indicating little, if any, mobility.

What is significant is that for the second and third examples-that is,where the variation is lower than for the high mobility example-thevariation is less than it would have been had the call admission controlalgorithm averaged together the supported data rate measurements acrossall of the terminals in the coverage area. And because the variation is,as a result, known to be lower for the particular basic service area,the call admission control algorithm does not have to be so conservativeand, as a result, more calls can be supported simultaneously in thatarea. Furthermore, the measurements of the terminals in past calls canbe applied to future calls, as the terminals involved in future callswill typically have a similar spatial distribution as the terminalsinvolved in past calls because the coverage and the usage in the basicservice area of interest remain more-or-less constant or, at least, tendto change only gradually.

It is to be understood that the above-described embodiments are merelyillustrative of the present invention and that many variations of theabove-described embodiments can be devised by those skilled in the artwithout departing from the scope of the invention. For example, in thisSpecification, numerous specific details are provided in order toprovide a thorough description and understanding of the illustrativeembodiments of the present invention. Those skilled in the art willrecognize, however, that the invention can be practiced without one ormore of those details, or with other methods, materials, components,etc.

Furthermore, in some instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringaspects of the illustrative embodiments. It is understood that thevarious embodiments shown in the Figures are illustrative, and are notnecessarily drawn to scale. Reference throughout the specification to“one embodiment” or “an embodiment” or “some embodiments” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment(s) is included in at least one embodimentof the present invention, but not necessarily all embodiments.Consequently, the appearances of the phrase “in one embodiment,” “in anembodiment,” or “in some embodiments” in various places throughout theSpecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, materials, orcharacteristics can be combined in any suitable manner in one or moreembodiments. It is therefore intended that such variations be includedwithin the scope of the following claims and their equivalents.

1. A method comprising: receiving: i) a plurality of data ratemeasurements, wherein the data rate measurements in said plurality areof the physical layer data rates that are supported over ashared-communications channel by one or more telecommunicationsterminals, and ii) a data-transmission requirement for a call that is toinvolve a first telecommunications terminal, wherein said firsttelecommunications terminal has transmitted at least part of saiddata-transmission requirement via said shared-communications channel;calculating a first measure of the variation in the distribution of afirst set of data rate measurements taken from said plurality, whereinthe data rate measurements in said first set are for a singletelecommunications terminal; and determining whether to admit said callon said shared-communications channel, based on (i) said first measureand (ii) said data-transmission requirement.
 2. The method of claim 1wherein said first measure is one of (i) a standard deviation and (ii) avariance.
 3. The method of claim 1 wherein the data rate measurements insaid plurality are of the physical layer data rates that are supportedover said shared-communications channel by two or moretelecommunications terminals when involved in calls.
 4. The method ofclaim 3 wherein at least one terminal has a first level of mobility andat least one terminal has a second level of mobility.
 5. The method ofclaim 1 wherein said data-transmission requirement specifies a firstcodec to be used for said call by said first telecommunicationsterminal.
 6. The method of claim 5 further comprising inferring a levelof mobility from said first codec specified by said data-transmissionrequirement.
 7. The method of claim 1 the determination of whether toadmit said call on said shared-communications channel is also based on aprobability being greater than a threshold value that the channeloccupancy of said shared-communications channel, as the result ofadmitting said call, will not exceed the available capacity, whereinsaid probability is derived from one or more probability distributions,wherein said one or more probability distributions comprise said firstmeasure.
 8. The method of claim 7 wherein the available capacity isbased on one or more utilization measurements of theshared-communications channel.
 9. A method comprising: receiving aplurality of data rate measurements, wherein the data rate measurementsin said plurality are of the physical layer data rates that aresupported over a shared-communications channel by one or moretelecommunications terminals; calculating a first measure of thevariation in the distribution of a first set of data rate measurementstaken from said plurality, wherein the data rate measurements in saidfirst set are for a single telecommunications terminal; and generating afirst distribution function of the channel occupancy of saidshared-communications channel, based on: i) said first measure, and ii)said plurality of data rate measurements.
 10. The method of claim 9further comprising: receiving a data-transmission requirement for a callthat is to involve a first telecommunications terminal, wherein saidfirst telecommunications terminal has transmitted at least part of saiddata-transmission requirement via said shared-communications channel;and determining whether to admit said call, based on said firstdistribution function; wherein the generating of said first distributionfunction is also based on said first data-transmission requirement. 11.The method of claim 10 wherein determining whether to admit said callcomprises evaluating a probability being greater than a threshold valuethat the channel occupancy of said shared-communications channel, as theresult of admitting said call, will not exceed the available capacity,wherein said shared-communications channel is already carrying (N-1)calls, wherein said probability is conditional on the value of N. 12.The method of claim 10 wherein said first data-transmission requirementspecifies a first codec to be used for said call by said firsttelecommunications terminal.
 13. The method of claim 12 furthercomprising inferring a level of mobility from said first codec specifiedby said data-transmission requirement.
 14. The method of claim 13wherein said first distribution function is also based on said level ofmobility.
 15. The method of claim 9 wherein the data rate measurementsin said plurality are of the physical layer data rates that aresupported over said shared-communications channel during two or morecalls.
 16. A method comprising: generating: a) a first distributionfunction of the physical layer data rates that are supported on ashared-communications channel; and b) a second distribution function ofthe channel occupancy on said shared-communications channel, based on:(i) said first distribution function, (ii) N calls concurrently usingsaid shared-communications channel, wherein N is a positive integer, and(iii) a first level of mobility; receiving an indication that a firsttelecommunications terminal is attempting to set up a call on saidshared-communications channel, wherein said first level of mobility isassociated with said first telecommunications terminal; determiningwhether to admit said call on said shared-communications channel, basedon said second distribution function, wherein said call is one of said Ncalls.
 17. The method of claim 16 further comprising: receiving a firstplurality of data rate measurements, wherein the data rate measurementsin said first plurality are of the physical layer data rates that aresupported over a shared-communications channel by a singletelecommunications terminal; and determining said first level ofmobility from the variation in the distribution of said data ratemeasurements in said first plurality.
 18. The method of claim 17:receiving a second plurality of data rate measurements; and determininga second level of mobility from the variation in the distribution ofsaid data rate measurements in said second plurality; wherein saidsecond distribution function is also based on said second level ofmobility.
 19. The method of claim 16 wherein said firstdata-transmission requirement specifies a first codec to be used forsaid call by said first telecommunications terminal.
 20. The method ofclaim 19 further comprising inferring said first level of mobility fromsaid first codec specified by said data-transmission requirement.